Production motor vehicles are required to pass various safety tests to ensure that they are sufficiently safe for use on public roads. In particular, it is desirable that the risk of injury to pedestrians is minimised in the event of a collision between a pedestrian and a motor vehicle, for example a collision between a pedestrian and hood or bonnet or other external surface of a motor vehicle. A standard test involves impacting a 3.5 kg impactor at 35 km/h at an angle of 50 degrees to a vehicle hood to determine the head injury criterion (HIC).
Motor vehicles are generally provided with a hood or bonnet, which is used to enclose the engine bay of a vehicle. The shape of the hood or bonnet is often formed to provide the required aerodynamic performance of air over the vehicle when it is being driven. In addition, the hood or bonnet is formed in view of aesthetic considerations. In addition, the hood may be provided with one or more vents or openings to permit air flow into the engine compartment of the vehicle in order to facilitate the provision of air to the air inlet of the engine or as cooling air. In addition, the hood may be provided with one or more ribs, bulges or other means in order provide strength and rigidity to the hood and/or to provide a larger volume in the engine bay under the hood. The hood or bonnet also provides a degree of structural rigidity across the front part of the vehicle. The hood or bonnet is frequently formed of an outer skin and an inner skin which may be formed from pressed steel or any other suitable material, e.g. composites or non-ferrous metals or alloys.
For maintenance, and sometimes to access a storage area, the hood or bonnet is often connected via a hinge to the vehicle structure in order that the bonnet or hood may be opened to provide access to the engine. Many different forms of hinge arrangement are known, for example hinges which permit the hood or bonnet to pivot forward or rearward of the vehicle. Frequently, in vehicles, a four joint hinge (four bar link) is provided in order to allow the bonnet or hood of the vehicle to pivot in a predetermined manner.
The hinge arrangement used to connect the hood or bonnet to the vehicle structure is frequently made of steel and is sufficiently rigid in order to support the hood or bonnet when it is opened. In some vehicles, often due to design constraints, the hinge arrangement can be located close to the upper outer skin of the bonnet or hood of the vehicle when the hood or bonnet is in a closed position. The part of the hood in the area of the hinge may therefore be more rigid that the areas of the hood between the hinges located on either side of the hood, creating stiffer potential impact points. Some vehicles are provided with active pedestrian protection systems, where the hood of the vehicle is displaced in a direction away from the engine. However, such systems require complex control systems.
US2008/0302591 discloses a passive pedestrian-protection front hood hinge. In the front hood hinge described, a cuttable device having a cuttable member is provided. A cutting knife is also provided. A stop determines the normal closed position of the hood. When a threshold value is exceeded, the stop is adapted to be disposed downwardly beyond the normal closed position against resistance generated by the cuttable device. The resistance is caused by the cuttable member being cut in the course of displacement of the stop upon movement of the cutting knife in relation to the cuttable member. However, the cuttable member remains intact, i.e. it does not break into more than one piece. Furthermore, as the cuttable member is cuttable, it does not fully fail either through ductile or brittle failure. It is difficult to know whether the arrangement remains in optimum condition, since hard bonnet slams or persons mistreating the vehicle by applying abuse loads such as excessive force during vehicle cleaning or polishing may thus cause a partial cutting which is not easily evident and so it is difficult to know whether the optimum impact performance will be provided at any time.
WO2010/086518 discloses an arrangement where hinges are provided with parts which flex or bend before any ultimate breakage. EP1205366 describes a hinge which deforms under collision in order to absorb energy.